JTAG circuit transferring data between devices on TCK terminals

Abstract

The present disclosure describes using the JTAG Tap's TMS and/or TCK terminals as general purpose serial Input/Output (I/O) Manchester coded communication terminals. The Tap's TMS and/or TCK terminal can be used as a serial I/O communication channel between; (1) an IC and an external controller, (2) between a first and second IC, or (3) between a first and second core circuit within an IC. The use of the TMS and/or TCK terminal as serial I/O channels, as described, does not effect the standardized operation of the JTAG Tap, since the TMS and/or TCK I/O operations occur while the Tap is placed in a non-active steady state.

1. An electrical system comprising:
 A. first and second devices each having a test access port interface including a test data input terminal, a test clock terminal, a test mode select terminal, and a test data output terminal; 
 B. a connection formed between the test clock terminals of the devices, the connection providing a test clock communication channel for data to be transferred between the two devices; and 
 C. circuit means in each of the first and second devices for transferring data between the two devices on the test clock communications channel while signals on the test mode select terminals of the devices are held at a low logic state. 
 
   
   
     2. The electrical system of  claim 1  wherein the first device is an integrated circuit and the second device is a controller. 
   
   
     3. The electrical system of  claim 1  wherein the first device is an integrated circuit and the second device is an integrated circuit. 
   
   
     4. The electrical system of  claim 1  wherein the first device is a core circuit within an integrated circuit and the second device is another core circuit within the integrated circuit. 
   
   
     5. The electrical system of  claim 1  wherein the data is transferred from the first device to the second device. 
   
   
     6. The electrical system of  claim 1  wherein the data is transferred from the second device to the first device. 
   
   
     7. The electrical system of  claim 1  wherein the data is transferred using Manchester data bit encoding.